1. Field of the Invention
The present invention relates to a display device using light emitting diode (LED) as a light source.
2. Description of the Related Art
For example, as disclosed in Japanese Patent Publication No. 2002-311417, priorly, cold cathode tubes have been used for light sources of liquid crystal display devices. As the light sources of liquid crystal display devices using cold cathode tubes, direct backlights and side backlights can be mentioned. And, in a liquid crystal display device with a built-in direct backlight, cold cathode tubes have been arranged on the rear surface-side of a liquid crystal panel, and a white light emitted from these cold cathode tubes passes through the liquid crystal panel, whereby an image is displayed. In addition, in a liquid crystal display device with a built-in side backlight, cold cathode tubes have been arranged at lateral sides on the rear surface-side of a liquid crystal panel, and a white light emitted from these cold cathode tubes is supplied to the entire surface of the liquid crystal panel by a light-guide plate, and this light passes through the liquid crystal panel, whereby an image is displayed.
In contrast thereto, recently, for example, as described in Japanese Patent Publication No. H04-118205, literature (Yourii Martynov et al., “High-efficiency slim LED backlight system with mixing light guide,” SID 03 DIGEST 43.3/Martynov, [on line], <URL: http://www.lumileds.com/pdfs/LEDBacklightMixingLightguideSID.PDF> [searched on Jun. 21, 2004]), and literature (Nikkei Electronics Jun. 21, 2004 Issue, pp. 60-61), in order to improve color reproducibility of images, a technique using red light emitting diodes, green light emitting diodes, and blue light emitting diodes as a light source has been developed. This technique is for arranging red light emitting diodes, green light emitting diodes, and blue light emitting diodes in line on the rear surface-side of a liquid crystal panel, mixing lights from these by a light guide, and irradiating the same as a white light onto a liquid crystal panel.
However, the aforementioned conventional technique has problems as shown in the following. Although light emitting diodes are more favorable in color reproducibility than cold cathode tubes, the light emitting diodes consume greater electricity than the cold cathode tubes, and the calorific value is also greater. Therefore, the light emitting diodes are raised in temperature by heat generated on their own. And, when the temperature is raised, the light emitting diodes are lowered in luminous efficiency. In addition, when the temperature of the light emitting diodes is excessively raised, the light emitting diodes themselves are destroyed.